ViewStub

1.ViewStub时一个大小为0，默认不可见的控件，只有给他设置成view.setVisible或者调用它的inflate方法才会填充布局资源，这样占用的资源比较少

2.应用

    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<Button
    android:id="@+id/show_bt"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="显示"/>

<Button
    android:id="@+id/hide_bt"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="隐藏"
    android:layout_alignParentRight="true"/>

<ViewStub
    android:id="@+id/viewStub"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerInParent="true"
    //这个Id时自己起的，通过这个id获取引入布局的view
    android:inflatedId="@+id/viewstub_layout"
    //引入的布局xml
    android:layout="@layout/stub_view"/>

 </RelativeLayout>

MainActivity

 public class MainActivity extends AppCompatActivity{

private Button show_bt,hide_bt;

private ViewStub viewStub;

private View  viewstub_layout;


@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    show_bt=findViewById(R.id.show_bt);

    hide_bt=findViewById(R.id.hide_bt);

    viewStub=findViewById(R.id.viewStub);

    show_bt.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
                try{
                    viewstub_layout=viewStub.inflate();
                    TextView viewstub_text=viewstub_layout.findViewById(R.id.viewStub_text);
                    viewstub_text.setText("显示了");
                }catch (Exception e){
                    viewStub.setVisibility(View.VISIBLE);
                }

        }
    });

    hide_bt.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            viewStub.setVisibility(View.GONE);
        }
    });


}
 }

viewStub调用两次inflate()会报错

QQ截图20190103154621.png

inflate()方法源码

   public View inflate() {
    final ViewParent viewParent = getParent();

    if (viewParent != null && viewParent instanceof ViewGroup) {
        if (mLayoutResource != 0) {
            final ViewGroup parent = (ViewGroup) viewParent;
            final View view = inflateViewNoAdd(parent);
            replaceSelfWithView(view, parent);

            mInflatedViewRef = new WeakReference<>(view);
            if (mInflateListener != null) {
                mInflateListener.onInflate(this, view);
            }

            return view;
        } else {
            throw new IllegalArgumentException("ViewStub must have a valid layoutResource");
        }
    } else {
        throw new IllegalStateException("ViewStub must have a non-null ViewGroup viewParent");
    }
}

因为获取不到viewParent 所以报错，所以最好时try...catch，但是可以通过setVisibility方法来控制显示与隐藏